The item he requests is random, so it's a good idea to save your game before going to bed the night before. If the item Thomas requests isn't something you can acquire, just reload your game and try again. Thomas will ask you for a new item that might be more attainable. If he asks you for a Golden Egg, that does not exist in Harvest Moon DS and it's a bug that entered when they made the game. Just reload like you normally would and have him ask for something new.
^^